Stent with smooth ends

ABSTRACT

A stent having at least one smooth end is disclosed. The stent may include a coating or coatings on one or both end portions to provide a smooth finish to reduce possible damage to body passages when the stent is deployed and delivered. The stent may also contain drugs or surgical adhesives or a combination thereof in or on the coated portion of the stent. The stent may also be of the type where the materials of the stent may be treated to have a smooth flexible end or ends. The stent may also be of a configuration such that at least one end is more flexible than the middle portion of the stent.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 09/072,944filed May 5, 1998, now abandoned the disclosure of which is herebyincorporated by reference.

FIELD OF THE INVENTION

This invention relates to a stent for use in body passages and moreparticularly, to a stent having at least one end which is coated or to astent having at least one end which is treated to be smooth andflexible. The invention also has particular relevance to a stent havingat least one end coated where the coating consists at least in part ofdrugs for delivery.

BACKGROUND OF THE INVENTION

Stents are used in human or animal body passages for maintaining thepatency of the passages. Stents are generally tubular in configuration,open ended and are expandable between a generally unexpanded insertiondiameter and an expanded implantation diameter. Stents are commonlyplaced or implanted by a mechanical transluminal procedure.

Prior art patents refer to the construction and design of stents as wellas apparatus for positioning stents within a vessel or other passage. Ingeneral, for example, such patents disclose a technique for positioningan elongated cylindrical stent at a region of stenosis, an aneurysm, orthe like. The stent expands as necessary to an implanted configurationafter insertion with the aid of a catheter.

Specifically, U.S. Pat. No. 4,733,665 to Palmaz discloses a number ofstent configurations for implantation with the aid of a catheter. U.S.Pat. No. 5,019,090 to Pinchuk discloses a generally cylindrical stentand technique for implanting it using a deflated balloon catheter toposition the stent. U.S. Pat. No. 4,503,569 to Dotter and U.S. Pat. No.4,512,338 to Balko et al. disclose a spring stent and a shape memoryalloy stent. There are also self-expanding stents such as thosedescribed in U.S. Pat. No. 4,732,152 to Wallsten et al. and U.S. Pat.No. 4,848,343 to Wallsten et al. All of these patents are herebyincorporated by reference.

It is important that the placement of the stent not contribute to orcause additional blocking. It is known that when stents are expanded totheir implantation diameter the ends of the stent may press into thevessel or cavity walls, especially the distal end of the stent. Thesharp or pointed edges and ends of some stents may then damage thewalls. Once damage has occurred, there is a likelihood that restenosiswill occur at these points where the stents ends and edges havepenetrated or pressed against the walls.

It is also known that stents may tear a passage wall and contribute torestenosis. This is particularly important for use of stents in bloodvessels. A tear in the vessel wall may cause blockage of the vessel.When the wall is torn a flap of tissue is created. The torn wall or flapusually is the source of the blockage. The flap falls into the passageand blocks it. It is then necessary to perform another procedure toremove the blockage and generally, another stent is needed to open thevessel or other passage.

Restenosis occurs in a number of cases where a stent has been used.Tearing of the wall of the passage or injury of the endothelial celllayer are possible causes of the restenosis. Therefore, it is desirableto utilize a stent which reduces the chances of a damaged vessel wall orbody passage which leads to further problems and further necessaryprocedures. However, current stents are not designed to reduce theoccurrence of cutting of vascular passages or the like.

In addition, it is known that a number of drugs may reduce the chance ofrestenosis. Therefore, the use of these drugs in combination with astent designed to reduce damage to body passages would be advantageous.However, known stents are not utilizing drugs with a means for reducingdamage to vessels and the like.

It is also known that bioadhesives may be used to repair tissue wallswhich may have been torn. However, current stents are not designed toavert a potential problem due to a tear. Currently, stents are notutilizing a bioadhesive with a stent to repair tissue walls and preventfurther medical procedures required because of the dissection of a bodypassage.

Consequently, a need remains for a stent which reduces the chances of atear or other damage of a body passage and which lessens the chances offurther required procedures. The present invention provides a stentwhich reduces the limitations of the prior stents with regard topossible tearing and the need for further treatment and therefore,performs in an improved fashion.

SUMMARY OF THE INVENTION

In accordance with a preferred embodiment of this invention a stent ischaracterized in that it includes at least one end coated with a desiredmaterial or materials. The coating may be of any desirable type whichlessens the chance of a tear in the passage, generally a coating with asmooth finish is preferred. Generally, any prior art stent may beimproved by providing it with a coating layer or layers of polymericcomposition on at least one end to provide a smooth finish. For anothertype, a stent may be provided with a sleeve which may be connected toone or both ends of the stent.

In another embodiment, the stent which has been coated or the stentwhich utilizes a sleeve may include bioadhesives and/or drugs to bedelivered to the site where the stent is implanted. It is known thatbioadhesives can be used to repair tissue walls. It is thereforedesirable to utilize a polymer coating to carry and deliver abioadhesive to the stent implantation location. In this manner, apotential problem can be averted by the presence of the bioadhesive inthe case of a tear or dissection. It is further known that a number ofdifferent drugs can be useful if delivered to the stent site. It isdesirable to deliver the drug or drugs with the stent when implantationis occurring or has occurred.

For yet another embodiment of the invention a stent is characterized inthat at least one end is constructed in a manner such that the end istreated to be smooth and flexible. The stent material may be heattreated, for example, or the design of the stent may be such that itprovides for flexibility on an end. Another embodiment includes a stentdesigned such that a looser mesh or pattern is utilized on the end orends of the stent and a tighter mesh or pattern is utilized in themiddle portion of the stent. These stents may also be coated on one orboth ends as well as materially treated.

Yet another embodiment of the invention a stent is constructed ofvarying materials having different degrees of flexibility. A more rigidmaterial is used in the center portion of the stent and a more flexiblematerial is used for one or both of the end portions of the stent. Thisembodiment may also be materially treated to increase smoothness orflexibility and may also be coated.

Stents according to the invention may be self-expanding or of the typewhich are expandable from a reduced diameter configuration by anexterior force (as opposed to self-expanding). The expandable stents maybe balloon expanding for example. Both types of stents are well known inthe art and need not be described in additional detail herein.

Stents according to this invention may be metal stents or polymericstents, the stent providing the basic framework for the device.

These and other advantages and features which characterize the inventionare pointed out with particularity in the claims annexed hereto andwhich form a further part hereof. However, for a better understanding ofthe invention, its advantages and objects obtained by its use, referenceshould be made to the drawings which form a further part hereof, and theaccompanying detailed description in which there is shown and describedan illustrative embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES

Referring to the drawings, wherein like numerals represent like partsthroughout the several views:

FIG. 1 is a perspective view of a stent according to the presentinvention;

FIG. 2 is a view of another stent according to one embodiment of thisinvention;

FIG. 3 is a cross sectional view taken along the line 3—3 of FIG. 2;

FIG. 4 is fragmentary view of an exemplary representation of a stentconfiguration, shown in flat plan view, which may be used with thisinvention;

FIG. 5 is an elevational view of one embodiment of a stent according tothe present invention;

FIG. 6 is a perspective view of another embodiment of a stent inaccordance with this invention;

FIG. 7 is a cross section taken along the line 7—7 of FIG. 6;

FIG. 8 is a perspective view of yet another embodiment of a stentaccording to this invention;

FIG. 9 is a perspective view of a further embodiment of a stent inaccordance with this invention;

FIG. 10 is a cross sectional view taken along the line 10—10 of FIG. 9;

FIG. 11 is a perspective view of another embodiment of the inventionutilizing a sleeve; and

FIG. 12 is an elevational view of another embodiment of a stentaccording to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the invention contemplates the use of a metal orpolymer stent which can have any configuration and may be any stenttaken from the prior art or any other stent. This stent is coated on atleast one end with an appropriate biocompatible coating to provide for asmooth end and edge.

Referring now to FIG. 1, a metal stent 10 is shown having a first endportion 12, a middle portion 14 and a second end portion 16. The stent10 may be stainless steel or any other metal or material as is known inthe art. In a preferred embodiment, the stent 10 includes a coating 18.The coating 18 is a biocompatible coating and has characteristics suchas a smooth surface and flexibility for better performance. The coatingmay be permanent or biodegradable. Most biodegradable coatings degradein the body within a few hours to a few years thereby serving thepurpose of preventing tears during angioplasty or deployment. In apreferred embodiment the coating 18 is polytetrafluoroethylene (PTFE orTEFLON) or polyethylene oxide. Many other suitable coatings may be usedwith the invention. The following is an exemplary list of coatings:

Hydrophilic polymer coatings, copolymers (block or graft) or theircross-linked versions (e.g. hydrogels), the polymers including:

poly(hydroxyethyl methacrylate) and derivatives; poly(vinyl alcohol);polyethylene oxide; polyethylene glycol; poly(propylene oxide);polyacrylamides; polyacrylic acid; polymethacrylic acid;poly(N-vinyl-2-pyrollidone); hydrophilic polyurethanes; poly(aminoacid);water soluble cellulosic polymers (sodium carboxymethyl cellulose,hydroxyethyl cellulose, for example); collagens; carrageenan; alginate;starch; dextrin; gelatins;

Biodegradable polymers;

poly(lactide); poly(glycolide); polydioxanone(PDS); polycaprolactone;polyhydroxybutyrate(PHBT); poly(phospazene); poly(phosphate ester);poly(lactide-co-glycolide); poly(glycolide-co-trimethylene carbonate);poly(glycolide-co-caprolactone); polyanhydrides;

Permanent coatings:

polytetrafluoroethylene(PTFE); polyurethanes; polyamides; polyesters;polyethers; polyketones; polyether ester elastomers; polyether amideelastomers; polyacrylate-based elastomers; polyethylene; polypropylene.

This list is exemplary only. Any appropriate coating may be used.

Placing the coating or layer(s) 18 on the stent 10 may be done by anyappropriate method such as dipping, painting, or spraying as is known inthe art. The thickness of the coating can be varied as desired toachieve different affects and if the material is biodegradable to lastfor different desired periods of time. An exemplary range of thicknessesis about 0.01-0.32 mm. The thickness chosen depends on the materialsused and the desired results. The thickness of the coating may vary. Forexample, the end of the stent may have a greater thickness than that onthe outer surface of the stent. This may provide more of a bufferbetween the stent end and a edge and the passage where it may be neededthe most. It is contemplated that one or more layers of coating may beapplied by appropriate known methods. The layers of coating may be thesame or may be coatings of different materials. Any appropriate coatingmaterials may be combined as desired.

The coating 18 is applied to at least the first end portion 12 of thestent 10. If desired, the coating 18 may also be applied to the secondend portion 16. The middle portion of the stent 10 remains uncoated inthe present invention. Generally, it is more important to coat thedistal end of the stent. This distal end is the end that first enters orengages the passage where the stent is needed. It is important that thestent not injure or tear the vessel wall as it is delivered to theproblem area. The coated stent provides for a smooth stent portion toreduce the chances of damage. It is sometimes desirable to coat theproximal portion of the stent instead of or in addition to the distalend. The same or different biocompatible coating or coatings may be usedto coat the distal and proximal ends.

The stent end portion or end portions may be coated on the outsidesurface 20, the inside surface 22, the side surface or surfaces 27, theend or ends 24 or the edge or edges 25. Depending on the configuration,the stent may have one or more end or side surfaces and one or moreedges 25. A stent of such a configuration is shown in FIGS. 1-5, forexample. The edges are created where two surface areas of the stentintersect such as the outer surface and the end surface; two endsurfaces; or an end surface and a side surface, for example. The edgesthat are coated may include any of the edges in an end portion of thestent. It should be understood that any one or any combination of thesesurfaces 20, 22, 24, 25, and 27 may be coated. Generally, it isdesirable to coat at least the end surface or surfaces 24 and the edgeor edges 25 most proximate to the ends 24. In order to ensure that thecoating adheres to the edge 25 of the stent at least a minimal portionof the outside or inside surface may also be coated. The coatings maycover any single area or combination of areas desired. When coating theoutside, inside, edge and /or side surfaces 20, 22, 25 and 27, a varyingportion of the length of the stent may be covered (length illustrated by1 in FIG. 1). When coating one end portion of the stent, such as thedistal end portion for example, anywhere from about 1% to 40% of thetotal stent may be coated. When coating both the distal and proximal endportions of the stent anywhere from about 2% to 80% of the stent may becoated. The length of the stent end portion(s) that is(are) coated willdepend on a number of factors including the coatings used, resultsdesired, stent application, etc.

The coating 18 may be applied such that a solid layer of coating coversthe stent end portion (similar to FIG. 11) or the coating may haveapertures or perforations which may or may not coincide with the patternof the stent (similar to FIGS. 1-10).

The coating 18 may also be used as a drug delivery system to preventrestenosis or for other treatment. The drugs may include radiochemicalsto irradiate and prohibit tissue growth. Angioplasty and stentdeployment may cause injury of the endothelial cell layer of bloodvessels, causing smooth muscle cell proliferation, leading torestenosis. To control smooth muscle cell growth endothelialization ofcells on the inner wall surface of vessels will prevent or prohibit thesmooth muscle growth. To stimulate endothelialization without provokingsmooth muscle cell proliferation human growth factors may be included inthe outer layer and delivered. Growth factors include VEGF, TGF-beta,IGF, PDGF, FGF, etc. These growth factors are dispersed in the matrix ofthe outer polymer coating 18 of the stent. All such materials arereferred to herein generally as “drugs”.

For carrying drugs, a gel-like material may be used. It may be appliedover the coating 18 or directly to the stent 10 and used as the coating18. There are two ways to apply drugs to such materials. The first wayis to mix the drug with the materials, then coat the mixture onto thestent. They can be cast as film or sheet with drug together, thenlaminate to the core stent. A second way is to coat or laminate polymerwith the core stent without the drug. The stent device is made, thensterilized. Due to their gel-like nature, the stent can then be insertedinto a drug solution. The drug will be absorbed into/onto the gel. Thestent can then be delivered into the body. The drug will then bereleased.

In one embodiment of the invention, the polymeric layer or coating 18may be polyethylene oxide containing Taxol™ (Paclitaxel). Other coatingsthat may be used with a drug may be polymers such as PGA/PLA, PEO/PLA orthe like containing a drug such as Taxol™ (Paclitaxel) or hydrogenperoxide.

Preferred gel like materials for use as a coating for the stent whendrug delivery is desired are polyethylene oxide, polyvinyl pyrrolidone,polyacrylates, and their blends or copolymers or lightly crosslinkedforms. Polyethylene glycol block copolymer with polylactides or otherpolyesters are examples. Hydrophilic polyurethane, poly(maleicanhydride-alt-ethylene) and their derivatives are examples. Othermaterials are polysaccharides and their derivatives. There are alsosodium alginate, karaya gum, gelatin, guar gum, agar, algincarrageenans, pectin, locust bean gums, xanthan, starch-based gums,hydroxy alkyl and ethyl ethers of cellulose, sodium carboxymethylcellulose. Some of the materials will be heated, then cooled, then a gelis formed. Some of the above are food gels. Some of them arebioadhesives.

Any drugs may be used, singly or in combination. For example, the drugscan be an anticoagulant, e. g. D-Phe-ProArg chloromethyl ketone. An RGDpeptide-containing compound, heparin, antithrombin compounds, plateletreceptor antagonists, antibodies, aspirin, urokinase, protaglandininhibitors, platelet inhibitors, or antiplatelet peptide. The drug canbe an inhibitor of vascular cell growth, DNA, RNA, cholesterol-loweringagents, vasodilating agents. The drug can be any drug such as Taxol™(Paclitaxel), 5-Fluorouracil, Beta-Estradiol, Tranilast, Trapidil,Probucol, Angiopeptin or any combination of them.

Since there are many drugs and many polymers, the stent can havemultiple layers of different polymers with the same or different drugs.For example, the stent can have two layers of the same polymer coating18 with one layer with drug and another layer without drugs. The stentmay have two layers of the same polymer with two different drugs asanother example.

In particular, various combinations of a cycling sinase inhibitoridentified as p21 and the vascular endothelial growth factor identifiedas VEGF, an endothelial nitrogen, may preferably be included in anddispensed from the coating polymer layer of a stent.

Incorporation of drugs and growth factors into a polymer layer can alsobe performed by several other methods, including the solvent method,melting method, soaking method and spraying method. If both polymer anddrug have a cosolvent, a solution case will be an easy way to providethe polymer matrix loaded with the drug or growth factor. If the polymercan be melted at low temperature and the drug or growth factor toleratesheating, a melting method can be used to mix the drug or growth factorinto the polymer matrix. Also, a polymer-drug solution or suspensionsolution can be used for coating to provide a layer containing the drugor growth factor.

In another embodiment of the invention the coating may be a film ofbioadhesive. Bioadhesives glue body tissue together. Using a bioadhesivefor the coating serves two purposes. The stent is smooth and if a tearhas occurred the tissue can be repaired. In this manner, blood flow willbe maintained in a vessel, for example. The bioadhesive may or may notalso have drugs loaded for delivery. Dissection, cutting or tearingoccurs in some stent and PTA or PTCA cases. Bioadhesives or surgicaladhesives may be used to repair the passage wall. However, these tearsor cuts are not necessarily discovered immediately. In those cases, afurther medical procedure must be undertaken to repair the wall. Thepresent invention eliminates some of these further medical procedures asa bioadhesive is included in the coating 18 which is delivered when thestent is deployed in place. The bioadhesive will repair damage to thevessel wall and it may not be necessary to undertake a further procedureto do the repair. The bioadhesive is chosen as the coating for the stentor is used in addition to a coating on the stent and is applied in aknown manner to one or both ends of the stent. The end or edge, side,outside and/or inside of the stent may utilize the bioadhesive.

Any appropriate bioadhesive may be used. For example, the followingbioadhesives may be used singly or in combination:

cyanoacrylate: ethyl cyanoacrylate, butyl cyanoacrylate, octylcyanoacrylate, hexyl cyanoacrylate;

fibrin glue: fibrinogen/thrombin/Factor XIII/calcium as catalyst

gelatin-resorcinol-formol (GRF) glue: formed from gelatin, resorcinoland water in the presence of formaldehyde, glutaraldehyde and heat (45°C.);

mussel adhesive protein, prolamine gel and transforming growth factorbeta(TGF-B);

polyacrylic acid, modified hypromellose, hydroxypropylmethyl cellulose,hydroxypropylcellulose, carboxymethyl cellulose, sodium alginate,gelatin, pectin, polyvinylpylindone, polyethylene glycol, aldehyderelative multifunctional chemicals, polyallylsaccharose, andpolypeptides.

Referring now to FIGS. 2 and 3, another metal stent is shown. An endportion of stent 26 is coated with a coating 28. Another embodiment ofthe invention includes a metal stent configuration such as the typeshown in part in FIG. 4. Both end portions of stent 30 are coated with acoating 32. These embodiments of FIGS. 2-4 include any appropriatecoating utilized as described above and the coating may contain drugsfor release and the coating may be a bioadhesive or include abioadhesive. The stent may be coated on the outer surface only or may becoated on the inner surface as well. The end or edge would also becoated, if desired. One or both ends of the stent may be coated.

It is also contemplated that a stent according to the invention may beof a polymeric material. The stents may be of any configuration and maybe of a biodegradable or nonbiodegradable polymeric material. A coatingor coatings as described above are utilized on one or both ends of thepolymeric stent to reduce injury to body passages and reduce restenosisand possible further medical procedures as described above. The coatingmay be multiple or single layers and be chosen from a variety ofsuitable biocompatible coatings. The coating may also include drugs fordelivery and/or a bioadhesive may be utilized.

Another stent is shown in FIG. 5. The stent is generally designated 34.The stent may be composed of a series of strands arranged in a crossingconfiguration which may be woven, braided or the like or alternativelyit may be formed of a polymeric sheet. The end portion of stent 34includes a coating 36. The coating may be applied by any variousstandard methods such as dipping, spraying, painting, etc.

FIGS. 6 and 7 show yet another stent configuration utilizing a coatingon one or both ends. The coil stent 38 includes a coating 40 on both thedistal and proximal end portions of the wire member which forms thestent in a preferred embodiment. The appropriate coatings describedherein may be utilized with this stent. The coating may be applied tothe wire member and then formed or the stent may be formed and lastly,the coating may be applied. Of course, the appearance of both types ofstent will differ. One or both end portions may be coated and thecoating may be applied to the various areas of the end portions asdescribed earlier.

FIG. 8 shows yet another stent form, a variation of which is shown inFIG. 9 and 10, the variation comprising apertures in a sheet like bodyportion. Both of these stents may be regarded as being formed from arolled up flat sheet comprised of a metal or a polymeric material havinga coating 42 on one or both end portions. The coating 42 is of the typedescribed in this application and may be applied to various areas of thestent as described herein.

Materials suitable for use in forming the polymeric stents to which theinvention relates are such that when fabricated to a desired geometrythey will afford the stent sufficient strength and support for theparticular intended use. Suitable materials do not produce toxicreactions or act as carcinogens. The preferred core polymeric stentmaterials are those such as are set forth below, which list is notexhaustive but exemplary only: Poly(L-lactide) (PLLA), Poly(D,L-lactide)(PLA), poly(glycolide) (PGA), poly(L-lactide-co-D,L-lactide) (PLLA/PLA),poly(L-lactide-co-glycolide) (PLLA/PGA), poly(D,L-lactide-co-glycolide)(PLA/PGA), poly(glycolide-co-trimethylene carbonate) (PGA/PTMC),polydioxanone (PDS), Polycaprolactone (PCL), polyhydroxybutyrate (PHBT),poly(phosphazene) poly(D,L-lactide-co-caprolactone) PLA/PCL),poly(glycolide-co-caprolactone) (PGA/PCL) and poly(phosphate ester).

Referring now to FIG. 11 another stent of the invention is shown. Thestent 44 includes at least one sleeve 46 which is designed andconfigured to fit over the end of a stent. The sleeve 46 is generallyhollow like the stent, having a flow passage therethrough. In thepreferred embodiment shown, the sleeve is a hollow cylindricalconfiguration which is connected to overlay the end portion(s) of thestent. The sleeve 46 shown in FIG. 11 overlays both the inside andoutside of the stent end when it is attached. The sleeve includes aninner wall 48 and an outer wall 50 having a space therebetween whereinthe inner wall 48 is adjacent the inside of the stent and the outer wall50 is adjacent the outside of the stent. In this manner, the sleeve 46receives the end of the stent in the space provided between the innerand outer walls. However, it is contemplated that the sleeve could be ofa design such that the inner surface of the stent is not covered. Thesleeve 46 may also be designed to be slightly longer in length than thestent body so that the sleeve extends beyond the end of the metal orpolymeric body. It should also be understood that the sleeve 46 may beof any configuration which will receive the end of any configured stent.Of course, stents of any configuration, shape and materials may beutilized.

The sleeve may be utilized on any stent configuration including, but notlimited to, those shown in the figures of this application. The sleevemay be made of any appropriate material as described herein and mayinclude drugs and/or a bioadhesive as discussed above. It should also beunderstood that it is also contemplated that the sleeve include one ormore layers of material including drugs and/or bioadhesives. Thematerials used may be permanent or biodegradable. It is furthercontemplated that the sleeve may have a solid wall as shown in FIG. 11or the wall may be perforated or may be of any design which may or maynot coincide with the design of the stent body. The sleeve may bedesigned to cover various lengths of the stent and if a sleeve isutilized on both ends of the stent they would not necessarily be of thesame length.

The sleeve may be bonded to the stent in a number of ways. The sleevemay be made of a material that has elastic properties so that it willstay in place on the stent end portion. The sleeve may also be bonded tothe stent by use of an adhesive. The adhesive would be an appropriatebiocompatible adhesive such as those bioadhesives listed earlier in thisdescription, for example, polyurethane and epoxy adhesive. It is alsocontemplated that the sleeve may be bonded to the stent by the use ofheat and pressure. In this manner, the stent will be partially embeddedin the sleeve.

Another embodiment of the invention contemplates the use of a metalstent where the stent end or ends have been formed and/or treated so asto be smooth and flexible. Any metal stent may be utilized including butnot limited to those shown in FIGS. 1-4. The stent would be manufacturedso that the ends would be more flexible and the edges or ends aresmoothed to eliminate any sharp edges, jagged areas, or bumps and thelike. In order to achieve the additional smoothness the stent may beelectropolished and/or tumbled. In this manner, the edges are rounded orsmoothed out so that the possibility of damage to a passage is lessened.The stent may also be heat treated to provide improved flexibility inthe end portions. The increase in flexibility also decreases the chancesof injury to a passage. The stent will bend more easily which willreduce damage which could be caused by a more rigid device. Methods forsmoothing articles are known in the art and other appropriate knownmethods may be used. It is known that heat treating will add flexibilityto a metal. Any other method which will provide enhanced smoothness andflexibility to the stent may be utilized.

For example, it is also contemplated that a stent with flexible ends maybe provided by utilizing a tighter mesh in the center portion of thestent and a looser mesh on one or both end portions of the stent. Anytype of mesh, pattern or braid may be utilized with this embodiment.Such a stent is shown in FIG. 12. The end portions 54 and 56 are of alooser configuration which allows for more flexibility in the endportions. Such a stent may also be treated by methods such as thosedescribed above to provide more flexibility and the stent may also betreated to provide for smooth edges or ends. Any stent pattern may bereconfigured to provide for more numerous or tighter struts in thecenter and less numerous or looser struts on one or both ends.

Another embodiment of a stent in accordance with the invention wouldinclude a metal stent which has been treated in accordance with theabove methods to be smooth and flexible and then is coated as describedearlier in this description.

Yet another embodiment of the invention is a metal stent where differentmaterials of varying flexibility are utilized for portions of the stentbody. Such a stent may be configured as shown in FIGS. 1-4 although anystent configuration is appropriate. In a preferred embodiment, such astent would be of stainless steel in the center portion. The endportions would be of Nitinol, a known nickel and titanium alloy. Nitinolis known to be more flexible than stainless steel. Other appropriatematerials may be utilized to provide flexible ends and a more rigidcenter portion which provides the strength needed in a stent. One orboth ends may be of a more flexible material than the center portion.Such a stent may also utilize the above mentioned material treatingmethods to provide more smooth and flexible ends. For example, ifNitinol ends are utilized, they may be heat treated to add flexibility.Such a stent may also include coated potions as discussed above.

Any of the above described embodiments may be utilized where appropriatein vascular or nonvascular, respiratory, gastrointestinal, rectal,urethral, and vaginal routes.

The above Examples and disclosure are intended to be illustrative andnot exhaustive. These examples and description will suggest manyvariations and alternatives to one of ordinary skill in this art. Allthese alternatives and variations are intended to be included within thescope of the attached claims. Those familiar with the art may recognizeother equivalents to the specific embodiments described herein whichequivalents are also intended to be encompassed by the claims attachedhereto.

What is claimed is:
 1. A stent comprising a main body portion having afirst end portion, a second end portion, a middle portion and a flowpassage defined therethrough, at least a portion of the first endportion and at least a portion of the second end portion having abiocompatible coating, the biocompatible coating comprising a polymer ora drug, wherein the biocompatible coating on the first end portiondiffers from the biocompatible coating on the second end portion themiddle portion free of the biocompatible coating.
 2. The stent of claim1 wherein the first end portion comprises an inner surface, an outersurface, an end and an edge, the coating covering the first end and atleast a portion of the edge of the first end portion.
 3. The stent ofclaim 2 wherein the first end portion is more flexible than the middleportion.
 4. The stent of claim 1 wherein the biocompatible coatingcomprises a polymer and a drug.
 5. A stent comprising a main bodyportion having a first end portion, a second end portion, a middleportion and a flow passage defined therethrough, wherein the first endportion is made of a first metal and the middle portion is made of asecond metal different from the first metal, at least a portion of thefirst end portion having a biocompatible coating, the biocompatiblecoating comprising a polymer or a drug, the middle portion free of thebiocompatible coating.
 6. The stent of claim 5 wherein the first endportion is made of Nitinol and the middle portion is made of stainlesssteel.
 7. The stent of claim 6 wherein the second end portion is made ofNitinol.
 8. A stent comprising a main body portion having a first endportion, a second end portion, a middle portion and a flow passagedefined therethrough, at least a portion of the first end portion havinga biocompatible coating, wherein the coating comprises a plurality oflayers the biocompatible coating comprising a polymer or a drug, themiddle portion free of the biocompatible coating.
 9. The stent of claim8 wherein the plurality of layers is comprised of the same coatingmaterial.
 10. The stent of claim 8 wherein the plurality of layers iscomprised of different coating materials.
 11. A stent comprising a mainbody portion having a first end portion, a second end portion, a middleportion and a flow passage defined therethrough, and a sleeve ofbiocompatible material connected to the first end portion, the sleeveincluding at least one layer of a material selected from the groupconsisting of bioadhesives and drugs, the middle portion of the stentfree of the at least one layer of material.
 12. The stent of claim 11wherein the stent comprises a looser mesh first end portion than themiddle portion.
 13. The stent of claim 11 wherein the first end portionis made of a first metal and the middle portion is made of a secondmetal different from the first metal.
 14. A stent comprising a pluralityof portions including axially spaced first and second portions, thefirst portion made of a first metal and the second portion made of asecond metal different from the first metal, wherein the first metal isNitinol and the second metal is stainless steel.
 15. The stent of claim14 wherein the stent has a first end, a middle and a second end, thefirst metal forming the first end, the second metal forming the middle,the stent further including a third portion displaced along the lengthof the stent from the first and second portions, the third portion madeof the first metal.
 16. The stent of claim 15 wherein the first andsecond ends are made of Nitinol, and the middle is made of stainlesssteel.
 17. The stent of claim 14 wherein the stent has a first end, amiddle and a second end and the first end is polished to provide asmooth first end relative to the middle.
 18. The stent of claim 17wherein the second end is polished to provide a smooth second endrelative to the middle.